1. Field of the Invention
This invention relates to magnetic transducers particularly applicable to magnetic disk drive systems. More particularly, the invention relates to thin film inductive read/write heads for ultra high density recording using a single lithographic step to define both a write coil and a pole structure.
2. Description of the Related Art
Thin film magnetic read/write heads are used for reading and writing magnetically coded data stored on a magnetic storage medium such as a magnetic disk or a magnetic tape. There is a continuing strongly-felt need for increasing the data storage density in such media. Most efforts to increase magnetic storage density involve techniques for increasing the areal bit density in the magnetic medium.
In rotating magnetic disk drives, the areal density is the product of the number of flux reversals per millimeter along a data track and the number of tracks available per millimeter of disk radius. Thus, high areal data storage density requires recording heads with high linear resolution and narrow track width.
A thin film inductive write head includes one or more coil layers imbedded in an insulation stack, the insulation stack being sandwiched between first and second pole piece layers. A write gap is formed in a pole tip region by provision of a gap layer between the pole pieces. The pole pieces are magnetically coupled in a back region. Between the pole tip region and the back gap region is a yoke region where the pole piece layers separate from one another to accommodate the insulation stack. The insulation stack typically includes a first insulation layer (I1) on the first pole piece layer, one or more coil layers on the first insulation layer, an additional insulation layer (I2) over the coil layer.
A combined head, such as a merged magnetoresistive (MR) head, includes the aforementioned write head as a write head portion combined with an MR read head portion. The MR read head portion includes an MR sensor which is sandwiched between first and second gap layers which are in turn sandwiched between first and second shield layers. In a merged MR head, a single layer serves a double function as a second shield layer for the read head and as a first pole piece for the write head. The combined head is carried on a slider which, in turn, is mounted on a suspension in a magnetic disk drive. The suspension is mounted on an actuator which moves the combined head over selected tracks on a rotating disk for reading and writing signals thereon. As the disk rotates a cushion of air is developed to provide an air bearing between the disk and the slider which counterbalances a loading force exerted by the suspension. A surface of the slider facing the disk is called an air bearing surface (ABS) and is typically spaced from the disk on the order of 0.02 xcexcm when the disk is rotating.
Future high data rate, high efficiency, inductive thin film write heads will need sub-micron resolution for both the coils and the poles. It is a well-known problem in the art of photolithography for head fabrication that as resist dimensions become smaller so do the specifications for resist coating uniformity, thickness depth of focus limitations and planarization repeatability, all of which are needed to avoid reflective artifacts and to obtain repeatability across the wafer. As yoke lengths in magnetic read/write heads shrink to dimensions less than 10 xcexcm, increasingly narrower pitch write coils must be fabricated where the line width of the resist image may be less than 0.5 xcexcm. The fabrication of the ferromagnetic write poles is also demanding on the same properties of the resist as well as tooling.
Accordingly, there is a strong felt need to improve the fabrication process to better define the poles as well as the coils in an ultra high density structure to meet the requirements of future high density magnetic recording heads.
It is an object of the present invention to disclose a ethod for making an inductive write head using a single lithographic step to define both a pole tip structure and a write coil that is coplanar with the pole tip structure.
It is another object of the present invention to disclose a method for making an inductive write head using a thin resist lithographic step and an image transfer technique for patterning the coplanar coils and pole tips.
It is yet another object of the present invention to disclose a method of making an inductive write head wherein the separation between the back end of a pole tip and the outermost turn of an inductive write coil is less than the final pole tip height.
It is a further object of the present invention to disclose a method of making an inductive write head wherein a first pole tip pedestal and a first inductive write coil layer coplanar with the first pole tip pedestal are defined in a first single lithographic step and wherein a second pole tip and a second inductive write coil layer coplanar with the second pole tip are defined in a second single lithographic step.
In accordance with the principles of the present invention, there is disclosed a method of making a read/write head having an inductive write head element whereby a second pole tip and an inductive write coil layer coplanar with the second pole tip are defined in a single thin resist lithographic step and image transfer process. The write head is formed over a magnetoresistive read head comprising a magnetoresistive sensor sandwiched between nonmagnetic insulative first and second gap layers which in turn are sandwiched between ferromagnetic first and second shield layers. An insulation layer is deposited over the second shield layer and a first write pole piece (P1) layer is defined and plated over the insulation layer. A photolithography step defines a first pole tip pedestal (P1P) at the ABS and the bottom element of a back gap element at the end of the first pole piece layer removed from the ABS. The P1P and back gap element are plated on P1 and a layer of inset insulation is deposited followed by a first planarization step, preferably a chemical-mechanical polish (CMP) process, to planarize the layer. After the planarization step, a write gap layer is deposited after which the gap material in the area of the back gap is etched out. A conductive seed layer is deposited over the P1P and the inset insulation. A hard-baked photoresist layer having a thickness greater than the desired thickness of the second pole tip (P2) or the write coil layer is deposited over the write gap/seed layer and the end of P1 removed from the ABS. A hard reactive-ion etchable (RIE) mask layer of RIE-able material such as TaOx, or alternatively Ta, Si or SiO2, is deposited on the hard baked photoresist layer and a thin image resist layer is formed on the hard RIE mask. Conventional high resolution lithography defines both P2 and the write coil structure coplanar with P2 in a single lithography step over the hard RIE mask. The image of the thin image resist is transferred via a fluorine containing plasma etch process into the underlying hard mask of, for example, TaOx.
Using an O2 plasma through the opening in the hard mask, a RIE of the hard-baked photoresist is done exposing the seed layer under the P2 and write coil areas. Resist is deposited to protect the coil part of the opened structure and the P2 tip and the part of P2 forming the upper layer of the back gap are deposited, preferably by plating, with a ferromagnetic material such as Nixe2x80x94Fe. The coil protection resist is removed and resist is deposited to protect the P2 tip and the back gap followed by deposition, preferably by plating, of the write coil with a conductive material such as copper (Cu). The coil protection resist is removed by development followed by removal of the hard-baked resist and the seed layer using suitable RIE processes. A planarizing layer of alumina is deposited over the entire structure followed by a second planarization step, preferably a CMP process, to planarize the structure at the desired thickness level of P2 and the write coil. A hard-baked resist layer is formed over the coil area to fill any voids in the planarizing alumina and to form an insulation layer between the coils and the subsequently formed pole (P3) structure connecting the P2 tip and the P2 back gap layer.
In another embodiment of the invention, there is disclosed a method of making a read/write head having a write coil that is plated before plating the pole piece. In this embodiment, the write coil is first plated with a conductive material such as copper (Cu). After the coil is plated and protected, the pole piece and back gap are plated with a ferromagnetic material such as NiFe.
In another embodiment of the invention, there is disclosed a method of making a read/write head having an inductive write head element with two write coils layers whereby a first pole tip pedestal (P1P) and an inductive first write coil layer that is coplanar with the P1P are defined in a single thin resist lithographic step and image transfer process over the P1 layer. A second pole tip (P2) and an inductive second write coil layer that is coplanar with the P2 are defined in a subsequent single thin resist lithographic step and image transfer process over a write gap layer deposited over the P1P and the first write coil.
In yet another embodiment of the invention, there is disclosed a method of making a read/write head having an inductive write head element with two write coils layers whereby a first pole tip pedestal (P1P) and an inductive first write coil layer coplanar with the P1P are defined in a single thin resist lithographic step and image transfer process over the P1 layer. A second pole tip (P2) and an insulation layer coplanar with the P2 are formed over the P1P and first write coil layer and a second write coil layer is formed over the insulation layer by processes known to the art.